Crystalline Hydrates Research Articles

Experimental studies for evaluation of the removal time of form on concrete using ultrasonic pulse velocity methods

In this study, the form removal time of concrete was evaluated using ultrasonic pulse velocity (UPV). The evaluation was performed based on the form removal strength specified in the American Concrete Institute (ACI), British Standard (BS), and Korean Construction Standards (KCS). Additionally, physical and mechanical properties of the concrete were evaluated from the early stages up to 28 days after casting. Specimens of both plain and lightweight concrete (LWC) were prepared for analysis. For the purpose of evaluating the concrete at various strengths, the water-to-cement (W/C) ratios were established at 0.41 and 0.28, aimed at achieving target compressive strengths of 30 MPa and 60 MPa for plain concrete, respectively. The measurement of mechanical properties was conducted through the assessment of penetration resistance, compressive strength, and ultrasonic pulse velocity (UPV). Models for predicting the strength based on regression analysis were proposed, taking into account the characteristics of the setting times (both initial and final). Additionally, the aggregate cross-section, matrix structure, and crystalline phases were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD). In the results of the experiments, it was observed that Mortar60 reached both initial and final set quicker than Mortar30, a phenomenon attributed to the higher cement content. Initially, Plain and LWC specimens exhibited comparable trends in compressive strength and ultrasonic pulse velocity (UPV). However, when examining the compressive strength development from 1 to 28 days, a notable difference of approximately 33 % was observed between Plain60 and LWC60. Similarly, differences in UPV ranged from 10.12 % to 11.88 %. The logistic regression model was found to predict the form removal strength more accurately than the exponential model, as indicated by the regression analysis results. When these results were compared with previous strength prediction models, the difficulty in predicting form removal strength became evident, primarily due to the substantial errors present in these models. Analysis using scanning electron microscopy (SEM) and X-ray diffraction (XRD) revealed the presence of hydration products within the lightweight aggregate, which signifies the hydration reaction. These products seemed to enhance the performance of the interfacial transition zone (ITZ) between the aggregate and cement paste. Furthermore, Mortar60 was characterized by larger crystalline hydration products, a denser matrix structure, and higher XRD peaks in comparison to Mortar30.

[formula omitted] Affects the crystalline calcium silicate hydrate minerals synthesized by fly ash-based silicon extraction solution and lime milk

When extracting amorphous silicon from fly ash using a strong alkaline solution, other elements such as Al also enter the silicon extraction solution in the form of AlOH4−. To systematically investigate the impact of AlOH4− on the synthesis of typical calcium silicate hydrate crystals in a silicon extraction solution, a specific amount of AlOH4− was added to the silicon extraction solution, and calcium silicate was hydrothermally synthesized at 90℃ and 230℃. Scanning electron microscopy (SEM) and Brunner−Emmet−Teller (BET) analysis revealed that with the increasing in AlOH4− content, microporous calcium silicate gradually loses its microporous morphology. While the specific surface area shows no significant change, the median pore diameter first increases from 1.47 nm to 1.58 nm and then decreases to 1.55 nm. The xonotlite fibers underwent a gradual refinement, diminishing from 0.28 to 0.15 µm. Simultaneously, the specific surface area increases from 28.87 to 56.8 m2/g. At an AlOH4− concentration of 3 mol/L, the microscopic morphology transforms into a sheet-like structure. X-ray diffraction (XRD) analysis reveals that AlOH4− promotes the formation of tobermorite while inhibiting the further development of calcium silicate. Additionally, Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance indicate that Al can replace Si in the calcium silicate hydrate system, primarily substituting positions the Q2 and Q3 sites. Qualitatively, it is suggested that with the increasing incorporation of Al, the polymerization degree of the silicon-oxygen tetrahedra decreases. According to experimental results, the concentration of AlOH4− should be below 0.05 mol/L when synthesizing microporous calcium silicate hydrate and less than 0.2 mol/L when synthesizing fibrous xonotlite-type calcium silicate hydrate.

Effect of Calcium on the Setting Time and Mechanical Property of a Red Mud-Blast Furnace Slag-Based Geopolymer.

This study aims to compare the effects of three calcium compounds on the workability, setting time and mechanical properties of red mud (RM)-blast furnace slag (BFS)-based geopolymers. The crystalline phase, hydration process and microstructure of RM-BFS-based geopolymers were characterized by X-ray diffraction (XRD), heat evolution, X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM) tests. The results showed that an appropriate amount of calcium compounds can improve the flowability and compressive strength of the geopolymers, but the excessiveness causes a decrease in strength due to rapid hardening. Other than calcium carbonate, both calcium oxide and calcium chloride played important roles in accelerating the setting times of RM-BFS-based geopolymers. The acceleration in the setting times of geopolymers could be attributed to the calcium hydroxide produced by the dissolution of the calcium compounds, which also provides nucleation sites for the geopolymerization reaction. This study gives new insights into the effect of calcium on the setting times and mechanical properties of geopolymers in the geopolymerization process.

Maximizing strength and durability in wood concrete (arbolite) via innovative additive control and consumption

AbstractA new approach for assessing the effectiveness and determining the consumption of additives to regulate the structural and mechanical characteristics of wood concrete is proposed, which allows rapid assessment in a short time and reduces the consumption of materials. The period is reduced from 28 to 1 day, and the sample sizes are reduced from 150 × 150 × 150 to 20 × 20 × 20 mm compared to those of the standard method. The results obtained are comparable using both methods within an error of up to 7%. The thermal conductivity of wood concrete with the addition of potassium sulfate was 20.8% less than that with the addition of calcium chloride. This reduction will reduce wall thickness, material consumption, and cost by 20.8%. In this regard, potassium sulfate, which does not form crystalline hydrates and makes it possible to obtain a material with lower thermal conductivity than other additives, all other things being equal, has a new advantage for wood concrete. In addition, potassium sulfate reduces the risk of corrosion of cement stone because one of the main causes of corrosion is crystalline hydrates. Reducing the risk of corrosion will increase the durability of the material.

Carbon dioxide hydrate crystallization thickening & morphology in a micro-confined environment for carbon capture & sequestration processes

Carbon dioxide capture and sequestration (CCS) are critical processes that are necessary to mitigate the impacts of climate change. In pipelines used for CCS and for ocean sequestration, the formation of CO2 hydrates can occur and be detrimental to the safety and integrity of the CCS equipment and process. Understanding the crystallization thickening behavior of CO2 hydrates is vital for understanding hydrate formation in CO2 pipelines and in other CCS applications, such as sequestration and CO2 capture or storage. In this study, a microfluidic chip reactor was used to crystalize and thicken CO2 hydrates at the channel walls. The morphology of the CO2 hydrates was visually analyzed and quantified using in situ Raman spectroscopy. Two hydrate layers were consistently observed. An annealed, dense layer of hydrate shared an interface with liquid water, while a porous hydrate layer shared an interface with CO2 gas. Capillary-like pore spaces could be observed in the porous layer, which confirms one proposed mechanism for hydrate film thickening. Subcooling (0.5–1.5 K), pressure (2.51, 3.10 MPa), and flow rate of CO2 (0.167, 1.67 mm3/s) were studied for their impact on the overall CO2 hydrate film thickness over time. Over the ranges of these chosen parameters, only CO2 flow rate was found to have a significant impact on the thickening of CO2 hydrates, and a higher flow rate led to thicker crystalline hydrate films. A first principles mass transfer model for hydrate film thickness was developed and applied to the measurement data collected for overall hydrate film thickness.

Physical, Mechanical and Microstructural Characteristics of Perlite-Based Geopolymers Modified with Mineral Additives

One of the promising raw materials for the synthesis of geopolymers is perlite, which is a natural low-calcium aluminosilicate. This research studied the physical, mechanical and microstructural characteristics of perlite-based geopolymers modified with different mineral additives that were prepared using different methods of introducing the alkali components and curing conditions. The experimental results of the consolidated perlite-based geopolymer pastes showed that curing conditions and the method of introducing the alkali component into the geopolymer matrix had a minimal effect on the average density while demonstrating a significant boost in compressive strength. So, after thermal treatment, the compressive strength increased by 0.63 to 11.4 times for the mixes when fresh alkali solution was used and by 0.72 to 12.8 times for the mixes with the 24 h conditioned alkali solution. Maximum-strength spikes from 1.1 MPa to 13.2 MPa and from 0.7 MPa to 9.7 MPa were observed for the mixes with kaolin when prepared with fresh and conditioned alkali solutions, respectively. It was also observed that thermal treatment facilitates the compaction of the matrix structure by 18% and 1% for the non-modified mix and the mix modified with Portland cement. Perlite-based geopolymers modified with Portland cement and citrogypsum demonstrated a significant reduction in the initial and final setting times with both methods of introducing the alkali solution. On the surface of mixes modified with citrogypsum, regardless of the curing conditions and method of introducing the alkali component, an efflorescence substance was observed. The microstructural analysis of the consolidated geopolymer perlite-based pastes containing citrogypsum demonstrated a loose structure and the presence of efflorescence, which can be associated with a retardation in interaction processes between alkali cations and the aluminosilicate component. EDS analysis demonstrated that the presence of such elements as oxygen, sodium and sulfur may indicate the efflorescence of unreacted sodium hydroxide (NaOH), citrogypsum (CaSO4) and the products of their interaction in the form of crystalline hydrates of sodium sulfate (Na2SO4).

ВЛИЯНИЕ ПЛАСТИФИКАТОРА НА ПРОЦЕССЫ ПЕРЕКРИСТАЛЛИЗАЦИИ ПРИ ТВЕРДЕНИИ ДВЕНАДЦАТИКАЛЬЦИЕВОГО СЕМИАЛЮМИНАТА КАЛЬЦИЯ

The mechanism of structure formation during hydration of duodecalcium semialuminate in the presence of plasticizer is considered. The purpose of the study was to determine the influence of polycarboxylate-based plasticizer on the formation and morphology of the hydrate phases formed. The object of the study was the mineral duodecalcium semialuminate 12CaO-7Al2O3 of stable α-form, having cubic syngony and plasticizer on polycarboxylate basis. The structure of cement stone was studied using X-ray phase and electron microscopic analysis. The mechanism of structure formation during hydration of duodecalcium semialuminate 12CaO∙7Al2O3 in the presence of plasticizer is presented, which consists in the formation of finely dispersed poorly crystallized hexagonal crystals of calcium hydroaluminate. The presence of superplasticizer in the composition of hydrated calcium aluminate slows down the nucleation and growth of crystalline hydrates due to the film formed on the surface of the interface between liquid and solid phases, creating a structural and mechanical barrier, which leads to slower saturation of the liquid phase, but promotes the formation of a greater number of crystallization centers and simultaneous growth of small crystals of both hexagonal and cubic habitus.

ОСОБЕННОСТИ ВЗАИМОДЕЙСТВИЯ ГЕМИНА И ZnII-КОМПЛЕКСА ТЕТРА(4 ПИРИДИЛ) ПОРФИРИНА С ГЕКСАМОЛИБДЕНОНИКЕЛАТ-ПОЛИАНИОНОМ В ВОДНЫХ СРЕДАХ

This work presents a method for producing new hybrid supramolecular organic-inorganic systems based on tetrapyrrole compounds (natural and artificially synthesized porphyrins) and hexamolibdenonicelate anion to create highly ordered supramolecular complexes based on porphyrins with the possibility of using them in medicine. In particular, the reaction of natural porphyrin (hemin) and the ZnII-complex of tetra(4-pyridyl)porphyrin with the heteropoly compound sodium hexamolibdenonicelate crystalline hydrate Na4[Ni(OH)6Mo6O18]·8H2O in an aqueous medium is considered. This heteropoly compound due to its physicochemical and biological properties can be considered as a part of photochromic materials and pharmacological agent. The optical absorption spectra of the obtained hybrid supramolecular organic-inorganic systems were investigated with the help of electronic absorption spectroscopy. Both the transformation of the bands which are the characteristics of porphyrins and the appearance of new bands indicating the formation of hybrid supramolecular organic-inorganic complexes are observed in the electron absorption spectra. The work traces the role of structural features of porphyrins in the process of their interaction with the heteropolyanions. Differences in the spectral behavior of the two metalloporphyrins when interacting them with the heteropoly compound have been shown and explained by variability in their structure. The data obtained will be useful when developing new hybrid materials as antibacterial components for medical use.

Preparation of complex titanium-containing coagulants from large-scale mineral concentrates and their use in wastewater treatment

Relevance. Development of new, highly effective reagents for treatment of wastewater of various origins is a complex and extremely important task. An equally pressing issue remains the development of technologies for processing large-scale mineral products, which currently have not found an economically feasible technology for their processing and have received the status of “waste”. The development of a technology for producing reagents using waste as a raw material will not only have an economic effect but will also significantly minimize the level of negative impact on the environment and take a step towards the implementation of the Zero Waste concept. Aim. Development of technology for processing large-scale titanium-containing raw materials to obtain complex titanium-containing reagents and study of their effectiveness in wastewater treatment from various industries. Methods. To study the phase composition of the samples, the X-ray diffraction method was used, and the determination of metal content in acidic solutions and wastewater was carried out by atomic emission spectroscopy. Results and conclusions. The authors have proposed the technology for production of complex titanium-containing coagulants, which includes hydrometallurgical technology for sulfuric acid processing of large-capacity mineral raw materials – titanite. Aluminum hydroxide was introduced into the resulting solutions to adjust the chemical composition and neutralize free sulfuric acid. The resulting aluminum sulfate transforms into the most stable form of 18-aqueous crystalline hydrate, absorbing moisture from the solution, realizing chemical dehydration. The study of the composition of solid samples of coagulants showed that the predominant phase in the composition of the complex coagulant is aluminum sulfate, and the content of titanium compounds ranges from 1 to 14 wt %. It was established that by varying the ratio of mineral raw materials:sulfuric acid it is possible to vary the amount of modifying additive titanium compounds in the complex reagent. It was proven that the use of complex titanium-containing coagulants in wastewater treatment allows reducing the consumption of coagulants by 25–35%, increasing the efficiency of water purification, minimizing residual concentrations of pollutants, and also significantly increasing the rate of sedimentation of coagulation sludge in comparison with traditional sulfate aluminum.

Modeling oceanic sedimentary methane hydrate growth through molecular dynamics simulation.

The crystallization process of methane hydrates in a confined geometry resembling seabed porous silica sedimentary conditions has been studied using molecular dynamics simulations. With this objective in mind, a fully atomistic quartz silica slit pore has been designed, and the temperature stability of a methane hydrate crystalline seed in the presence of water and guest molecule methane has been analyzed. NaCl ion pairs have been added in different concentrations, simulating salinity conditions up to values higher than average oceanic conditions. The structure obtained when the hydrate crystallizes inside the pore is discussed, paying special attention to the presence of ionic doping inside the hydrate and the subsequent induced structural distortion. The shift in the hydrate stability conditions due to the increasing water salinity is discussed and compared with the case of unconfined hydrate, concluding that the influence of the confinement geometry and pore hydrophilicity produces a larger deviation in the confined hydrate phase equilibria.

Preference of curing regimes based on fire resistance of ultra-high performance cementitious materials (UHPCM) mixed with fly ash

The cement-fly ash (FA) binary system was prepared as the ultra-high performance cementitious materials (UHPCM), and the effect of curing regimes on the evolution of microstructure and compressive strength of UHPCM at elevated temperatures was investigated. The results showed that multi-stage combined curing (MC) could remarkably improve the compressive strength of UHPCM at ambient temperature, which attributed to the further hydration of cement and the pozzolanic reaction of FA to produce more stable hydrates. However, steam curing (90 °C for 7 d) was more conducive to the residual compressive strength growth and retention of UHPCM exposed to elevated temperatures. The mechanism of this phenomenon was revealed by XRD and SEM analysis. The further hydration and conversion reactions occurred mainly inside the steam cured specimens when exposed to fire temperature, and a large number of C–S–H gels were gradually transformed into crystalline hydrates with high strength, excellent thermal stability and different forms, which made the microstructure denser and thus had better fire resistance. Comparatively, a large number of crystalline hydrates were generated prematurely in dry-hot air cured specimens, which made the decomposition reactions dominate under fire, resulting in coarsening of microstructure and reduction of macroscopic mechanical strength of UHPCM continuously.

Preparation of multicomponent rare earth based oxide charges

In this study we describe a relatively facile synthetic approach for the production of multicomponent oxide charges as the precursors of quaternary barium-rare earth-copper selenides BaRECuSe3, which, in turn, are of interest as promising thermoelectric materials. The starting reagents were initially prepared, including cleaning of the surface of elemental copper and annealing the rare earth oxides RE2O3 in a high-temperature furnace. A mixture of double, ternary and quaternary oxide charges was prepared by dissolving the stoichiometric ratios of the starting reagents RE2O3:2Cu:2Ba(NO3)2 (RE = La, Nd, Gd, Dy, Ho, Y, Er, Tm, Yb, Lu), CeO2:Cu:Ba(NO3)2, Pr6O11:6Cu:6Ba(NO3)2 or Tb4O7:4Cu:4Ba(NO3)2 in nitric acid. The Ce-based oxide charge was obtained in the presence of H2O2 as a reducing agent to improve solubility in nitric acid. Then, cocrystallization of crystalline hydrates, followed by their dehydration, and destruction of the resulting (oxo)nitrate salts, and dispersion of the final polycrystalline samples were performed. According to the powder X-ray diffraction data, topochemical reactions led to the formation of heterometallic oxides BaxREyCuzOn, BaREO3, BaCuO2 and RE2CuO4. The developed synthetic approach allows to obtain the target phase of orthorhombic selenides BaRECuSe3 of three structural types BaLaCuS3, Eu2CuS3 and KZrCuS3 with high yields in a relatively short period of time and at lower temperatures in comparison to the previously used synthetic methods.

Phase and microstructure evolution of the hydration products of magnesium phosphate cements under sulfuric acid environments

Magnesium phosphate cement is a good canditate of repairing material served under harsh environments and its acid resistivity has drawn a lot of interest, but rare detailed research on the evolution of its physiochemical features has been reported. In this work, the impacts of sulfuric acid solution (pH = 2 – 7) on the hydration products of magnesium potassium phosphate cement and magnesium ammonium phosphate cement. Results showed that the main hydration products, struvite/struvite–K, experienced partial corrosion in the absence of the sulfuric acid solution replacement. The phase transition of struvite–K is clearly visible, leading to the formation of the new crystalline hydration product Mg3(PO4)2•22 H2O. The initial blossoms cluster microstructure transformed into a diffused dispersion that resembled a plate. When the solution was replaced, struvite/struvite–K underwent significant corrosion and even complete decomposition in more acidic (pH = 2, 3) solutions.

Investigation of encapsulated water wire within self-assembled hydrophilic nanochannels, in a modified γ4-amino acid crystals: Tracking thermally induced changes of intermolecular interactions within a crystalline hydrate

Nanostructures formed by the self-assembly of modified/unmodified amino acids have the potential to be useful in several biological/nonbiological applications. In that regard, the greater conformational space provided by γ-amino acids, owing to their additional backbone torsional degrees of freedom and enhanced proteolytic stability, compared to their α-counterparts, should be explored. Though, modified single amino acid-based nanomaterials such as nanobelts or hydrogels are developed by utilizing the monosubstituted γ-amino acids derived from the backbone homologation of phenylalanine (Phe). Examples of a single γ-amino acid-based porous nanostructure capable of accommodating solvent molecules are not really known. The crystal structures of a modified γ4(R)Phe residue, Boc-γ4(R)Phe-OH, at different temperatures, showed that hydrogen-bonded water molecules are forming a wire inside hydrophilic nanochannels. The dynamics of intermolecular interactions between the water wire and the inner wall of the channel with relation to the temperature change was investigated by analyzing the natural bonding orbital (NBO) calculation results performed with the single crystal structures obtained at different temperature points. The NBO results showed that from 325 K onward, the strength of water–water interactions in the water wire are getting weaker, whereas, for the water–inner wall interactions, it getting stronger, suggesting a favorable change in the orientation of water molecules with temperatures, for the latter.

Влияние кристаллогидратов солей в огнетушащем порошковом составе на его удельную эффективность тушения легковоспламеняющейся жидкости

The article presents the comparative evaluation of specific fire extinguishing efficiency of powder compositions containing crystalline hydrate salts as a gas-generating component. Thermodynamic calculations and experimental tests have shown a reduction in the consumption of powder compositions for extinguishing highly flammable liquids by at least 30% when hexahydrate of magnesium-ammonium phosphate MgNH4PO4∙6H2O is used as a component of fire extinguishing powders. The research has shown the advantage of implementing fine particles of crystalline hydrates (d<10 μm) obtained during the controlled precipitation process compared to analogs manufactured by mechanical grinding (d < 100 μm).

Amorphous-like thermal conductivity and high mechanical stability of cyclopentane clathrate hydrate.

The thermal conductivity κ of cyclopentane clathrate hydrate (CP CH) of type II was measured at temperatures down to 100 K and at pressures up to 1.3 GPa. The results show that CP CH displays amorphous-like κ characteristic of many crystalline clathrate hydrates, e.g., tetrahydrofuran (THF) CH. The magnitude of κ is 0.47 W m-1 K-1 near the melting point of 280 K at atmospheric pressure, and it is almost independent of pressure and temperature T: ln κ = -0.621-40.1/T at atmospheric pressure (in SI-units). This is slightly less than κ of type II CHs of water-miscible solvents such as THF. Intriguingly, unlike other water-rich type II clathrate hydrates of water-miscible molecules M (M·17 H2O), CP CH does not amorphize at pressures up to 1.3 GPa at 130 K and also remains stable up to 0.5 GPa at 240 K. This shows that CP CH is mechanically more stable than the previously studied water-rich type II CHs, and suggests that repulsive forces between CP and the H2O cages increase the mechanical stability of crystalline CP CH. Moreover, we show that κ of an ice-CH mixture, which often arises for CHs that form naturally, is described by the average of the parallel and series heat conduction models to within 5% for ice contents up to 22 wt%. The findings provide a better understanding of the thermal and stability properties of clathrate hydrates for their applications such as gas storage compounds.

НАПРЯМКИ ПОКРАЩЕННЯ ОСНОВНИХ ХАРАКТЕРИСТИК ТЕПЛОВИХ АКУМУЛЯТОРІВ ТА ТЕПЛОАКУМУЛЯЦІЙНИХ МАТЕРІАЛІВ

The article is devoted to the study of heat storage technologies as the main energy saving measure. The paper conducts a patent search and analyzes scientific papers that cover the issue and present the main material of existing technologies for thermal energy storage. The classification of the main types of heat accumulators (HA) and heat storage materials (HSM) is presented. Heat accumulators are classified: by the nature of accumulation; by the level of operating temperatures; by the duration of the charge-discharge period. The differences and design features of TAMs, advantages and disadvantages are analyzed. The main heat storage materials that are actually used or can be used in the future are identified. The thermophysical properties of heat storage materials, such as specific heat capacity, melting point, density, and density, are described.
 The methodology for calculating the volume of capacitive and phase-transition heat accumulators is determined based on the following initial data: the type of heat storage material, the type and thermal characteristics of the heat carrier, and the temperature drop of the heat storage material. Examples of the practical use of capacitive batteries are given, in particular, a tank battery in a solar heating system, as well as a gravel battery in a solar vegetable garden. The use of crystalline hydrates and organic low-melting compounds (fatty acids and paraffins) as phase-transition heat storage materials is described. The characteristics of thermochemical thermal accumulators, their principle of operation, and their advantages over capacitive and phase-transition accumulation units are presented. The reactions of enrichment of traditional carbon fuels are described, and examples of reactions that can be used as heat storage processes are given. Prospects for further research are identified.

Theoretical and experimental approach on investigation of ethylurea-water clusters

Abstract Alkylated urea derivatives have found wide application as starting materials for the production of many drugs, including anticancer drugs, as well as in many other areas. In this work, we studied ethylurea crystalline hydrates using a complex of theoretical and experimental methods. The nature of the intermolecular interactions between ethylurea and water molecules is investigated using topological analyses such as atoms in molecules (AIM), non-covalent interaction (NCI), reduced density gradient (RDG), electron localized functions (ELF), and localized orbital locator (LOL). The hydrogen bond energy is in the range of 1.1295–14.4327 kcal/mol. Also, a highly correlated parabolic relationship between topological parameters (E HB, ρ, and ∇2 ρ) and H-bond length was determined. According to RDG data, with an increase in the number of water molecules in ethylurea clusters, the area corresponding to hydrogen bonds increases. The initial ethylurea and its crystalline hydrate were studied by FTIR spectroscopy and X-ray diffraction. The introduction of water molecules into the ethylurea crystal was proved by IR spectroscopy by the appearance of the corresponding absorption bands. X-ray diffraction showed that the initial ethylurea has intense peaks at 11.2, 16.8, 21.4, 22.24, 25.06, 25.78° 2Ɵ, the intensity of which changes when water molecules are introduced into the crystal.

Accelerated aging resistance, abrasion resistance and other properties of alkali-activated slag mortars containing limestone powder

The Earth's crust is widely recognized for its abundance of limestone (LS). Limestone powder (LSP) has a wide range of potential properties that make it suitable for various applications and fields. It has found extensive usage in Portland cement-based materials. Recently, the incorporation of LSP into geopolymers is becoming more of a concern than before and has become a hot topic. In this article, high range of LSP (2.5–50 wt%) was introduced into alkali-activated slag (AAS) mortars activated with NaOH and sodium silicate solution as a substitution of slag. For the first time, the effect of LSP on the accelerated aging resistance and abrasion resistance of AAS mortars was examined. In addition, the typical traditional routine properties such as flowability, setting time, mechanical strength, water absorption, and total porosity were studied. Sophisticated equipment was utilized to observe the changes in crystalline phases, hydration products, and microstructures of selected samples. The results showed higher flowability and longer setting time with including LSP. As the amount of LSP increased as the flowability and setting time increased. The introduction of 2.5–25% LSP positively affected the mechanical strength, aging resistance, abrasion resistance and transport properties. In contrast, the introduction of 35% did not show an essential change, whilst the introduction of 50% LSP negatively affected the mentioned properties.

Formation of Neptunium(V) Carbonates: Examining the Forceful Influence of Alkali and Alkaline Earth Cations.

Herein, neptunium(V) carbonates containing sodium or potassium cations were synthesized via chemical precipitation. Various techniques such as scanning electron microscopy, energy-dispersive X-ray spectroscopy, thermogravimetry combined with differential scanning calorimetry, X-ray diffraction, and X-ray absorption spectroscopy were used to analyze the microstructures and elemental compositions of these samples. The crystal structures of hydrated NaNpO2CO3·3H2O (P1, a = 4.3420(2) Å, b = 4.8962(2) Å, c = 10.0933(11) Å, α = 91.014(7)°, β = 77.834(11)°, and γ = 90.004(10)°) and KNpO2CO3 (P63/mmc, a = b = 5.0994(2) Å, c = 10.2210(15) Å) were determined for the first time using the Rietveld method. The synthesized carbonates exhibited distinct structural features and decomposition behaviors, as demonstrated through thermogravimetry analysis, which revealed the presence of crystalline hydrate water in sodium neptunium(V) carbonate. Furthermore, calcium-containing neptunium(V) carbonates were synthesized and characterized. Samples with the general composition Ca0.5NpO2CO3 were obtained using the ion exchange method and chemical precipitation from solutions containing competing cations (Ca2+, Na+, K+, and Mg2+). The synthesis conditions notably affected the diffraction patterns of the obtained calcium neptunium(V) carbonates. This investigation enhances our understanding of the structural properties and thermodynamic stability of neptunium(V) carbonates in the presence of diverse cations commonly found under radioactive waste disposal conditions.